Building a bird: musculoskeletal modeling and simulation of wing-assisted incline running during avian ontogeny

Flapping flight is the most power-demanding mode of locomotion, associated with a suite of anatomical specializations in adult birds. In contrast, many developing birds use their forelimbs long before acquiring "flight adaptations", to enhance leg performance and, in some cases, fly. How does anatomical development influence these behaviors? To address this question, we used biomechanical modeling and simulation techniques to analyze the ontogeny of pectoral limb function in a ground bird. Our simulations suggest that immature birds have excess muscle capacity and are limited more by feather morphology, possibly due to differences in growth. These results provide critical information about the ontogeny and evolution of avian locomotion by (i) establishing how muscular and aerodynamic forces interface with the skeletal system to generate movement in developing birds, and (ii) providing a benchmark to inform modeling and simulation of other locomotor behaviors, both across living species and among extinct avian ancestors.